Synthesis, characterization, and promoter effect of Cu-Zn/γ-Al2O3 catalysts on NO reduction with CO

The role of the Zn promoter and the preparation route in the catalytic properties of Cu-Zn/γ-Al2O3 catalysts towards NO reduction with CO were investigated in this study. The catalysts were prepared by chemical reduction of the corresponding metal species (Cu(NO3)2·2.5H2O and Zn(NO3)2·6H2O) by a liquid polyol solution. The nano-bimetallic catalysts were obtained through this method, in which heterogeneous nucleation by seeding the reactive medium with foreign nuclei, Cu, was synthesized by the addition of an easier reductive metallic precursor to replace the homogeneous nucleation. Several samples were prepared with a variation in the reduction temperature, reduction time, Cu/Zn atomic ratio, and Cu and/or Zn loading weight in the catalysts. The morphology and surface chemical structure of the samples were assessed by transmission electron microscopy (TEM), BET surface area measurements, and X-ray photoelectron spectroscopy (XPS). Based on TEM evidence, the Cu-Zn/γ-Al2O3 catalysts were found to be composed of a spherical Cu-Zn nanoparticle, and the particle size decreased with the addition of Zn. XPS was used to study the different chemical states of the Zn-promoted Cu/γ-Al2O3, which indicated that the concentration of the reduced Cu species was related to the addition of Zn, thus increasing the NO conversion. The results obtained suggest that the use of Zn as a promoter and the polyol method as a preparation route played important roles in the properties of the catalysts, the Cu particle size, the reduction/oxidation efficiency of Cu/Zn, and the catalytic properties of NO reduction with CO.